Engines, such as diesel engines and dual-fuel engines, include ports and valves to regulate the entrance and exit of air, fuel, and exhaust into and out of the engine cylinders. The cylinders of some uniflow scavenged two-stroke dual-fuel engines include intake ports that are opened by movement of a piston and allow for introduction of air and gaseous fuel, as well as one or more exhaust valves for removing post-combustion exhaust from the cylinder. The exhaust valve cyclically opens and closes to control the flow of exhaust out of each cylinder. The opening/closing profile of an exhaust valve, relative to crankshaft angle, is commonly known as valve timing. Valve timing, including the degree to which a valve is open (e.g., amount of lift), relative to crankshaft angle, may be depicted as a lift profile.
Conventional exhaust valve timing and lift profiles have been known to cause blow-by in some dual-fuel engines. Blow-by is the reverse flow of exhaust from the cylinder through the intake ports to an air-box, just as the intake ports are opened. As air flows from a compressor outlet through the air-box and past each cylinder, it is heated by the hot exhaust that escapes from the cylinders during blow-by. In some instances, this may create a temperature difference along the air-box of about 5-20° F. In some engines, this temperature difference can cause pre-ignition of gaseous fuel in the cylinder(s) furthest from the compressor due to the higher temperature. During pre-ignition, gaseous fuel burns before liquid fuel is injected into the combustion chamber. Thus, pre-ignition can cause the engine to operate inefficiently.
Some engines include variable valve timing devices configured to adjust the timing of an exhaust valve of a diesel engine according to different parameters. For example, Japanese Patent Document JPS 58152140 published on Sep. 9, 1983 (“the '140 document”) discloses a variable valve timing device that controls the opening of an exhaust valve depending on operating conditions of the engine. Specifically, the variable valve timing device includes an actuator that is activated to change the time at which the exhaust valve opens.
While the variable valve timing device of the '140 document may allow for adjustment of the time when an exhaust valve opens to alter peak cylinder pressure after combustion, it may not be applicable to inhibiting pre-ignition of gaseous-fuel caused by blow-by. In particular, since the variable valve timing device of the '140 document does not allow for control of a cylinder pressure specifically at a time that an intake valve is opened, it may remain susceptible to creation of a pressure differential that allows for blow-by. In other words, even though peak cylinder pressure may be adjusted by the device of the '140 document, cylinder pressure at a time when blow-by occurs (e.g., when intake ports are opened) is not controlled. The '140 document does not include a control system and/or exhaust system that would allow for such control.
The disclosed fuel system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.